331CI Chevy Small-Block Engine – Horsepower

331CI SMALL-BLOCK CHEVY, 486 HP at 6,900 RPMJeff Latimer, Valencia, CAThere are certain engine combinations that just work. In the history of the small-block Chevy, the little 327 has been passed over in the rush to Mouse motors of larger and larger displacement. But Jeff Latimer hasn’t forgotten. He works at one of our favorite machine shop haunts, Jim Grubbs Motorsports, and has built a series of small-displacement, high-revving street small-blocks mostly just because he likes them. His latest adventure is this 0.030-over 327 that will eventually find a home in his meticulously detailed ’63 Chevy II. Combine a 4.030-inch bore with a short 3.25-inch stroke crank with good heads and a big cam and you can expect this motor to rev-6,900 rpm to be exact. But Jeff planned it that way. He expected it to do well, but not as well as the 486 hp this little spinner actually produced. Better yet, it makes peak torque at 4,900, which gives this mini-Mouse a 2,000-rpm powerband spread between peak torque and peak horsepower. If all that isn’t enough, this equates to 1.47 hp/ci. Listen closely and you can just imagine the sound of this tight small-block powershifting through all three gear changes.

DYNO CHART

RPM

TQ

HP

3,500

357

238

3,700

351

247

3,900

342

254

4,100

330

257

4,300

343

281

4,500

374

320

4,700

383

343

4,900

392

366

5,100

418

406

5,300

415

419

5,500

409

428

5,700

408

443

5,900

402

452

6,100

399

464

6,300

395

473

6,500

390

483

6,700

379

484

6,900

367

482

Peak HP: 486 @ 6,600

CamshaftWhile you might think that this minibeast has a roller cam, the 331 relies instead on a Comp flat-tappet Magnum hydraulic cam spec’ing out at 244/244 degrees at 0.050 with 0.534-inch lift with the bigger rockers. Instead of a chain, Jeff went with a Comp Cams wet-belt system that is hidden behind the aluminum two-piece timing cover. Because this was an early block he had to do some machine work to make the belt work, but it was used to improve valvetrain stability at high rpm.

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HeadsThose are AFR 180cc Eliminator aluminum cylinder heads with 2.02/1.60-inch stainless valves. Jeff added a set of Comp Cams beehive PN 26915 springs along with flyweight titanium retainers, using the “soft approach” to valve control, since Jeff knew this short-stroke screamer would spin up to 7,000. For rockers, he chose a set of Comp 1.6:1 rollers along with 71/416-inch ARP studs. Manley supplied the 0.080-wall-thickness pushrods. The valve covers are chromed Z28 pieces with K&N breathers.

Short-Block“My plan was to build a long-rod, short-stroke motor that would rev to 7,000,” Jeff says. That includes a stock factory large-journal 327 crank ground 0.020- and 0.030-under on the mains and rods respectively. Then he used an off-the-shelf JE 6.0-inch-rod 383 piston (1.125-inch compression height) and combined it with a 6.250-inch Eagle I-beam rod. The 11/416-inch ring package on the piston is moved up so that even with the short compression height, the oil rings don’t intrude into the wristpin hole. Compression is 10.5:1 with the flat, two-valve relief piston because Jeff pushed them 0.005 inch out of the hole using 0.036-inch-thick Cometic head gaskets.

InductionThat’s a Professional Products Hurricane single-plane intake manifold with a 1-inch spacer below that Holley 750-cfm Street HP carburetor. Jeff tried a dual-plane thinking it would improve torque, but this high-rpm package much preferred the single-plane for peak power. Jeff saw a 22hp increase (464 went to 486) when he added the single-plane intake and spacer combo.

LubricationWhile you might expect some exotic oil pan tricks, Jeff says, “All I did was buy a ’69 Camaro Z/28 oil pan and windage tray and bolt it on,” and he added a Melling oil pump with the trick bolt-on pickup tube. He also ran the same break-in oil for the dyno tests, using Chevron’s straight 30W Delo engine oil.

IgnitionThat may look like a stock HEI on the outside, but remove the cap and you see that Jeff has updated this stocker with an MSD module, rev limiter, and coil along with MSD wires.

ExhaustJGM runs all its dyno tests with open exhaust due to space considerations. Those are 131/44-inch dyno headers, so Jeff can expect to lose some peak horsepower to a full exhaust system, but that takes little away from this motor’s bragging rights.